The present invention, in some embodiments thereof, relates to phosphotriesterase (PTE) enzymes capable of hydrolyzing nerve gases and, more particularly, but not exclusively, to V-type nerve gases.
At present, both prophylaxis and post-intoxication treatments of chemical warfare nerve agent (CWNA) poisoning are based on drugs selected to counteract the symptoms caused by accumulation of acetylcholine in cholinergic neurons. Current antidotal régimes consist of pretreatment with pyridostigmine, and of post-exposure therapy that involves administration of a cocktail containing atropine, an oxime reactivator and an anticonvulsant drug such as diazepam. The multi-drug approach against CWNA toxicity has been adopted by many countries and integrated into their civil and military medical doctrines. However, it is commonly recognized that these drug régimes suffer from several disadvantages that call for new therapeutic strategies. The preferred approach is to rapidly detoxify the CWNA in the blood before it has had the chance to reach its physiological targets. One way of achieving this objective is by the use of bioscavengers. However, use of the best stoichiometric bioscavenger currently available (human butyrylcholinesterase, hBChE) requires administration of hundreds of milligrams of protein to confer protection against toxic doses of CWNA. A safer and more effective treatment strategy can be achieved by using a catalytic bioscavenger to rapidly degrade the intoxicating OP in the circulation.
The promiscuous nerve-agent hydrolyzing activities of the enzyme phosphotriesterase (PTE) make it a prime candidate both for prophylactic and post exposure treatment of nerve-agent intoxications. However, efficient in-vivo detoxification using low doses of enzymes (≤50 mg/70 kg) following exposure to toxic doses of nerve agents, requires that their catalytic efficiencies (kcat/KM) towards the toxic nerve agent isomers will be increased.
PTE variants that can efficiently hydrolyze V-type nerve agents are disclosed in Cherney et al, 2013, ACS Chem Biol 8: 2394-2403. In-vivo post-exposure activity of one of these variant was demonstrated in guinea-pigs intoxicated with a lethal dose of VX (Worek et al, 2014, Toxicol Lett 231: 45-54).
Additional background art includes U.S. Pat. No. 8,735,124.